At a sampling rate of 32000 samples/sec, 100 samples 100/32000 = .003125 seconds.
Between samples 50 and 150 there are approx. 7 cycles,
so the dominant frequency in that region is 7/.003125 = 2240 hz.
The detector divides by 16, so the bat is actually emitting at
16*2240 = 35840 hz.
This also agrees with the sonogram, as it should.